High luminance light emitting devices capable of short-wave emission in the blue light region have long been expected, and this sort of light emitting devices have recently realized by using AlGaInN-base materials. Rapid progress has also been made in application to full-color light emitting devices and display devices, based on combination with red and green high luminance light emitting devices. AlGaInN-base materials cannot, however, avoid increase in the cost because they are mainly composed of Ga and In, which are relatively rare-existing metals. Another big problem is that the material need growth temperature of as high as 700 to 1,000° C., causing a considerably large energy consumption for the manufacture. This is undesirable not only from a viewpoint of cost reduction, but also because it is against the current public situation where energy saving and suppression of the global warming are extensively discussed. Japanese Laid-Open Patent Publication No. 2001-44500 discloses a light emitting device configured by growing a more inexpensive MgZnO-base compound semiconductor layer grown in a hetero-epitaxial manner on a sapphire substrate.
Growth of the MgZnO-base oxide by vapor phase growth process such as MOVPE (metal organic vapor phase epitaxy) process under an atmosphere with a reduced pressure is, however, likely to produce oxygen deficiency causative of excessive electrons, and this make it difficult to form a p-type or intrinsic-semiconductor-type (also referred to as “i-type” taking the first letter of “intrinsic”) MgZnO-base oxide layer which is indispensable for composing the light emitting device.
Many of conventional light emitting devices are configured by placing a p-type cladding layer on the light extraction surface side. A metal electrode disposed on the p-type cladding layer side in this case is formed so as to cover only a part of the light extraction surface thereof, so as not to interfere light extraction as possible. It is also generally accepted to preliminarily grow, on the p-type cladding layer, a current spreading layer which is raised in the in-plane conductivity through a heavy doping of a p-type dopant, and then to form the metal electrode on the current spreading layer, in order to prevent the emission drive current from concentrating in regions around the metal electrode.
As for the light emitting device using the ZnO-base compound semiconductor, even preparation of the p-type semiconductor having a conductivity as large as the cladding layer level is not easy due to influence of the above-described oxygen deficiency, so that it is readily predicted that a far larger difficulty will be encountered in preparation of a high conductivity MgZnO-base compound semiconductor increased in the p-type dopant concentration as being suited for current spreading, and this will make the light emitting device disadvantageous in every aspects of quality, performance, yield ratio and production efficiency.
A subject of the this invention therefore is to provide a MgaZn1-aO-base light emitting device excellent in the light extraction efficiency, having a light emitting layer section composed of a MgaZn1-aO-type oxide, and a high conductivity MgZnO-base compound semiconductor layer disposed on the light extraction surface side thereof.